Pressure applicator devices particularly useful for non-invasive detection of medical conditions

ABSTRACT

A probe for application to a body part particularly a finger of a patient to detect a change in the physical condition of the patient includes a housing defining a compartment closed at one end and open at the opposite end for receiving the distal end of the patient&#39;s finger and a medium wholly self-contained within the probe for applying a static pressure field substantially uniformly around the distal end of the patient&#39;s finger, of a predetermined magnitude sufficient to substantially prevent distention of the venous vasculature, uncontrolled venous backflow, and retrognade shockwave propagation into the distal end, and to partially unload the wall tension of, but not to occlude, the arteries in the distal end when at heart level or below. A sensor senses changes in the distal end of the patient&#39;s finger related to changes in arterial blood volume therein.

This application claims foreign priority from Israel Application No.124787 filed in Israel on Jun. 7, 1998, which application isincorporated by reference as if fully set forth herein.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to pressure applicator devices forapplying a predetermined static pressure to a body part of a patient.The invention is particularly useful as a probe for application to adigit (ie., a finger or toe) of a patient for the non-invasive detectionof certain medical conditions in accordance with the method described inour PCT Application PCT/IL97/00249; and the invention is thereforedescribed below especially with respect to such applications.

Our Application PCT/IL97/00249 (WO98/04182, published Feb. 5, 1998 whichis incorporated by reference as if fully set forth herein) disclosesmethods and apparatus for the non-invasive detection of a change in aphysiological condition of a patient by monitoring changes in theperipheral arterial tone as manifested by changes in the arterial bloodvolume in a terminal extremity of a body part, preferably a digit(finger or toe) of the patient. The method and apparatus are describedin that application particularly for detecting mycardial ischemia andsleep apnea, and also for the continuous monitoring of blood pressure.The described apparatus includes a probe for application to thepatient's body part (e.g., finger) which probe includes a housing forreceiving the distal end of the patient's body part, and pressurizingmeans for applying a static pressure field substantially uniformlyaround the distal end of the patient's body part when received in thecompartment, including its terminal-most extremity. The static pressurefield is of a predetermined magnitude sufficient to substantiallyprevent distention of the venous vasculature, uncontrolled venousbackflow, and retrograde shockwave propagation into the distal end ofthe body part, and to partially unload the wall tension of, but not toocclude, the arteries in the distal end of the body part when at heartlevel or below. The probe further includes a sensor within the housingfor sensing changes in the distal end of the patient's body part relatedto changes in volume therein due to changes in instantaneous bloodvolume related to arterial tone.

That application described a number of probe constructions in which thestatic pressure field was applied via a remotely located pressure sourceconnected by tubing to a fluid chamber within the probe. However,utilizing such remotely-located pressure sources complicates theconstruction of the apparatus and also restricts the mobility of thepatient.

OBJECTS AND BRIEF SUMMARY OF THE PRESENT INVENTION

An object of the present invention is to provide a device particularlyuseful as a probe in the method and apparatus of the above-cited PCTApplication but of a simplified or improved construction as compared tothe devices described therein. Another object is to provide a probewhich does not restrict the mobility of the patient.

According to broad aspect of the present invention, there is provided adevice for application to a digit of a patient to detect a change in thephysical condition of the patient; the device comprising a probeincluding: a housing defining a compartment closed at one end and openat the opposite end for receiving the distal end of the patient's bodypart; pressurizing means for applying a static pressure fieldsubstantially uniformly around the distal end of the patient's bodypart, when received in the compartment, including the extreme distal tipof the patient's body part, which static pressure field is of apredetermined magnitude sufficient to substantially prevent distentionof the venous vasculature, uncontrolled venous backflow, and retrogradevenous shockwave propagation into the distal end, and to partiallyunload the wall tension of, but not to occlude, the arteries in thedistal end when at heart level or below; and a sensor for sensingchanges in the distal end of the patient's body part related to changesin volume thereof due to changes in instantaneous blood volume relatedto arterial blood volume therein; characterized in that the pressurizingmeans for applying the static pressure substantially uniformly aroundthe distal end of the patient's body part, including its terminal-mostextremity, is constituted of a medium wholly self-contained within theprobe.

A number of embodiments are described below for purposes of example.

According to further features in one class of embodiments describedbelow, the pressurizing means includes an inner resilient membranewithin the housing and defining therewith an inner chamber to be filledwith a fluid for applying the static pressure via the membranesubstantially uniformly around the distal end of the patient's bodypart, including its terminal-most extremity.

According to further features in the latter described embodiments, thepressurizing means further includes an outer resilient membrane attachedto the housing externally thereof and defining therewith an outerchamber communicating with the inner chamber via openings in the housingfor enlarging the effective volume of the inner chamber such as to causethe inner membrane to apply substantially the same static pressurearound the distal end of the patient's body part despite changes involume therein.

A further embodiment is described below for purposes of example, whereinthe pressure means includes a body of resilient sponge material formedwith a recess defining the compartment for receiving the patient's bodypart when inserted therein.

The sensor within the housing is described below, for purposes ofexample, as being either an optical sensor for optically detecting, or aHall Effect sensor for magnetically detecting, volume changes in thesubject's finger which attend pulse-related blood volume changes andcorresponding finger girth changes.

As will be described more particularly below, the present inventionenables probes to be constructed with the static pressurizing meanswholly self-contained within the probe housing, thereby greatlysimplifying the construction of the probe as well as reducingrestrictions on the mobility of the patient using such a probe. However,the invention may also be implemented in a two-section probe wherein onesection includes a first housing attached to the body part and defininga part of the static pressurizing means, and the second section includesa second housing having another part of the static pressurizing means influid connection to the first section, the sensor being located withinthe second section.

While the invention is particularly useful in the methods and apparatusof the above-cited PCT Application, the invention, or various featuresthereof, can be used in other applications as will also be describedbelow.

Further features and advantages of the invention will be apparent fromthe description below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1 is a longitudinal sectional view, and FIG. 1a is a correspondingview but rotated 90° with respect to FIG. 1, illustrating one form offinger probe constructed in accordance with the present invention;

FIG. 2 is a graph of volume versus pressure, and

FIG. 3 is a graph of pressure versus time, both helpful in explainingthe operation of the finger probe of FIG. 1;

FIG. 4 is a view similar to that of FIG. 1, but omitting the sensor andillustrating a modification in the construction of the finger probe;

FIG. 5 is a view similar to that of FIG. 1, but illustrating anotherfinger probe constructed in accordance with the present invention;

FIGS. 6a-6 c diagrammatically illustrate one manner of applying theprobe of FIG. 5 to a patient's finger;

FIGS. 7a-7 c illustrate a modification in the construction of the probeof FIG. 5, and the manner of applying it to the patient's finger;

FIGS. 8a-8 c diagrammatically illustrate another probe constructed inaccordance with the present invention;

FIG. 9 is a side elevational view diagrammatically illustrating a probesimilar to that of FIGS. 8a-8 c but including another fasteningarrangement for fastening the two half-sections together;

FIGS. 10a-10 c are views corresponding to FIGS. 8a-8 c but illustratinganother probe constructed in accordance with the present invention;

FIGS. 11a-11 c illustrate another probe construction similar to that ofFIGS. 10a-10 c;

FIG. 12 illustrates one manner of applying to a patient the probe ofFIGS. 11a-11 c and a read-out to an electrical circuit;

FIGS. 13a-13 c diagrammatically illustrate another probe construction inaccordance with the invention and showing particularly the elements ofthe sensor and the manner of making electrical connections to them;

FIG. 14 illustrates a probe similar to that of FIGS. 1 or 4 butincluding a pressure cuff contiguous to the inner (proximal) end of theprobe for extending the pressure field with respect to the sensorelements;

FIG. 15 illustrates another construction of a probe in accordance withanother aspect of the invention;

FIG. 15a illustrates an overall apparatus including the probe of FIG.15;

FIGS. 16 and 16a diagrammatically illustrate another probe constructionin accordance with the present invention;

FIG. 17 illustrates an overall apparatus including any of the otherdescribed probes; and

FIGS. 18a-18 d diagrammatically illustrate a further probe constructionin accordance with the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 and 1a illustrate one form of probe constructed in accordancewith the present invention particularly for use in the method andapparatus of the above-cited PCT Application for monitoring theperipheral arterial tone of a patient's body part (e.g., digit) in orderto indicate, in a non-invasive manner, the physiological state ormedical condition of the patient. As briefly described above, and asmore fully described in the above-cited PCT Application, such a probeincludes pressurizing means for applying a static pressure fieldsubstantially uniformly around the distal end of the patient's digit,including its terminal-most extremity (extreme distal tip), and a sensorfor sensing changes in the distal end of the patient's digit related tochanges in volume thereof due to changes in instantaneous blood volumerelated to arterial blood volume therein. The probe illustrated in FIG.1, however, is of a simplified construction as compared to the probesillustrated in the above-cited PCT Application, since the staticpressure means in the probe of FIG. 1 is constituted of a medium whollycontained within the probe.

The probe illustrated in FIGS. 1 and 1a includes a housing 2 of rigidplastic material, closed at one end, and open at the opposite end, anddefining a compartment for receiving the patient's finger 3. An innermembrane 4 within housing 2 defines therewith a chamber 5 for receivinga fluid, such as air, which applies a static pressure fieldsubstantially uniformly around the distal end of the finger 3 includingits extreme distal tip. The probe illustrated in FIGS. 1 and 1a furtherincludes a sensor constituted of one part 6 a on one side of the finger,and another part 6 b on the opposite side, for measuring changes involume of the patient's finger caused by arterial blood flow. Theillustrated probe further includes a U-shaped restraining bar 7 fixed byan annular ring 8 within the housing to cause the inner membrane 4 tomore firmly grip the patient's finger 3 when inserted into the probe.

The above-cited PCT Application is hereby incorporated by reference forfurther details of the construction of the probe and the manner of itsuse for monitoring a physiological state or medical condition of thepatient.

The probe illustrated in FIGS. 1 and 1a, however, differs from thosedescribed in the above-cited PCT Patent Application in the manner ofproviding the substantially uniform static pressure applied around thedigital end of the patient's finger. Whereas in the examples illustratedin the above-cited PCT Application, such a static pressure is providedby a remotely-located pressure source coupled by tubing to the probe,the probe illustrated in FIGS. 1 and 1a includes a static pressurizingmeans which is wholly self-contained within the probe housing.

For this purpose, the probe illustrated in FIGS. 1 and 1a includes anouter resilient membrane 10 attached to the housing 2 externally thereofand defining with the housing an outer chamber 11. The outer membrane 10is of annular configuration and is applied around an annular portion ofthe housing spaced from its tip such that the outer chamber 11 is ofannular configuration. The outer annular chamber 11 communicates withthe inner chamber 5 by means of a plurality of openings 12 formedthrough housing 2.

The outer membrane 10 enlarges the effective volume of the inner chamber5 such as to cause, according to the Laplace Law, the inner membrane 4to apply substantially the same static pressure around the distal end ofthe patient's finger 3 despite changes in volume in chamber 5. Thus, theLaplace Law broadly states that the distending pressure (P) within adistensible hollow object is equal at equalibrium to the tension in thewall (T) divided by the two principal radii of curvature of the object(R1, R2); that is P=T (1/R1+1/R2). In a sphere, R1=R2; therefore P=2T/R.When the wall tension and the radius vary in direction proportion toeach other (i.e., T/R is constant), as is substantially the case forrubber balloons for most of the range above the minimum distention andbelow the maximum distention, the balloon distending pressure remainssubstantially constant irrespective of changes in volume.

FIG. 2 illustrates the relationship of pressure with respect to volumeand particularly shows the relatively large operating zone in which thepressure remains substantially constant with the changes in volume. Theactual pressure value is a function of the thickness and mechanicalcharacteristics of the distensible material.

The probe illustrated in FIGS. 1 and 1a effectively enlarges the volumeof the inner chamber 5 by the volume of the outer chamber 11communicating with the inner chamber via openings 12 in the housing 2such that the static pressure applied by the fluid within chamber 5remains substantially constant irrespective of changes in volume ofchamber 5 caused by arterial blood flow within the patient's finger 3received'within the probe. If the finger is partially removed fromwithin the probe, the remaining portion will still be subject to thesame external pressure because of the Laplace Effect.

The application of near diastolic counterpressures (40-70 mmHg), overthe entire surface of the distal phalanges of the finger, was found notto adversely affect tissue perfusion despite the knowledge thatlocalized pressure applied to tissues can cause collapse ofmicrocirculation. This is due to the fact that while arterial pressureexceeds the counterpressure permitting inflow of arterial blood, forblood to return via the veins venous pressure must overcome the appliedexternal pressure. The induced elevation of venous pressure causes theupstream microcirculation to be pressurized to a pressure levelintermediate between the outgoing venous blood and the incoming arterialblood; hence the transmural pressure of the microcirculation within theapplied pressure field is greater than zero and collapse of themicrocirculation is prevented.

The maintenance of fingertip surface temperature within a narrow rangearound 36° C., and the lack of a tendency for surface temperature tofall after 2 hours of 70 mmHg pressure application, supports the abovedescribed model of the preservation of microcirculatory patency andconsequently adequate tissue perfusion, as does the fact that overnightapplication of the pressurized probed on over 120 fingers in 60 subjectswas well tolerated with no deleterious effects.

In the probe illustrated in FIGS. 1 and 1a, the inner chamber 5 isinitially filled with the fluid via a port 13 having a one-way valve 14permitting the fluid (e.g., air) to flow into the chamber, but not outof the chamber. FIG. 3 illustrates how the pressure varies with time,and shows that after a fixed quantity of air has been added, thepressure within the device remains relatively constant over a 24-hourperiod.

FIG. 4 illustrates a probe of the same construction as described abovewith respect to FIGS. 1 and 1a, except that the sensor elements havebeen omitted for simplification purposes. Also, the port 13 and theone-way valve 14 have been omitted, and instead a fixed volume of fluidis permanently confined within the space defined by the internalmembrane 4 and the external membrane 10.

FIG. 5 illustrates a probe of similar construction as FIG. 4, exceptthat the outer membrane 20 is of tubular configuration to define anouter chamber 21 with the distal tip of housing 2. The outer chamber 21communicates with the inner chamber 5 via openings 22 formed in thehousing tip, so as to effectively enlarge the volume of the innerchamber to produce the relatively constant static pressure applied tothe subject's finger 3 irrespective of changes in volume, as describedabove. Although FIG. 5 does not include the refill port or one-wayvalve, corresponding to elements 13 and 14 in FIGS. 1 and 1a, theseelements could be included in which case they would be provided in theportion of housing 3 not covered by the outer membrane 21.

FIGS. 6a-6 c illustrate one manner in which the probe constructed as inFIG. 5 may be manipulated to allow the patient's finger 3 to be insertedinto the probe. For this purpose, housing 2 of the probe is providedwith an annular ring 23 on the rigid portion of the housing spacedinwardly (proximally) from the outer membrane 20. A syringe including acylinder 24 and a plunger 25 is used for shifting the fluid from theinner chamber 5 to the outer chamber 21 in order to permit the patientto insert the finger into the probe. FIG. 6a shows the open end ofcylinder 24 applied to ring 23; FIG. 6b, shows the plunger 32 a, 32 battached to the outer surface of the respective housing section todefine the two outer chambers 37 a, 37 b communicating with the twoinner chambers 35 a, 35 b via openings 38 in the housing sections. Thenon-hinged sides of the two housing sections carry “Velcro” (T.M.) loopand hook fastener strips 39 a, 39 b, to enable the two sections to betightly closed around the patient's finger 33 to apply the desiredpressure thereto.

FIG. 9 illustrates a two-section construction similar to that of FIGS.8a-8 c, except that, instead of using “Velcro” (T.M.) fastener strips 39a, 39 b to fasten the two sections together, the fastening elements inthe construction illustrated in FIG. 9 include tongues 40 a receivedwithin slots 40 b integrally formed in the contacting edges of the twohousing sections 32 a, 32 b.

FIGS. 10a-10 c illustrate another two-section probe construction, but inthis case the two half-sections 42 a, 42 b are hinged together at theadjacent edges of the two end walls 43 a, 43 b of each housing section.In addition, instead of using an integral hinge, the hinge is in theform of a flexible non-extensible strip 44 bonded to the two end walls43 a, 43 b. The two half sections are secured in their closed conditionsby two “Velcro” (T.M.) strips 45 a, 45 b fixed to one of the housingsections 42 a at the open end of the housing and engageable with strips46 fixed to the other housing section 42 b. In all other respects, theconstruction of the probe illustrated in FIGS. 10a-10 c is substantiallythe same as described above and includes the outer membrane defining theouter chamber communicating with the inner chamber to provide theabove-described Laplace behavior.

FIGS. 11a-11 c and 12 illustrate a probe 50 mounted on the finger of ahand 51 (FIG. 12). Probe 50 is of the two-section construction as inFIGS. 10a-10 c, and as more particularly illustrated in FIGS. 11a-11 c.The latter figures also illustrate the two-section inner membrane 53 a,25 being retracted within its cylinder 24, to thereby draw the fluidwithin the inner chamber 5 into the outer chamber 21, permitting thesubject to insert the finger into the probe, whereupon the plunger 25may be returned to its normal position within its cylinder 24; and FIG.6c shows the syringe being removed.

FIGS. 7a-7 c illustrate another manner of manipulating the probe of FIG.5 to permit insertion of the subject's finger. This is done by providingthe outer membrane 20 with a finger piece including a knob 26 externallyof the membrane and fixed to a backing member 28 engaging the innersurface of the membrane. Thus, knob 26 may be grasped by the user andpulled outwardly (FIG. 7b) to expand the outer chamber 21, thereby todraw into it the fluid from the inner chamber and to permit the patientto insert the finger 3 into the probe. After the patient's finger hasthus been inserted, knob 26 may be released, whereupon the probe willassume the operative position illustrated in FIG. 7c.

The function of the outer membrane 20 in the construction of FIGS. 7a-7c is to facilitate the Laplace behavior as in the previously describeddesigns.

FIGS. 8a-8 c diagrammatically illustrate a probe made of two sectionshinged together to enable the probe to be opened (FIG. 8b) and closedaround the patient's finger (FIG. 8c). Thus, as shown in FIG. 8a, thehousing, generally designated 32, is also of tubular configurationclosed at one end and open at the opposite end for the insertion of thefinger 33. In this case, however, housing 32 is split into twohalf-sections 32 a, 32 b joined together along their length by anintegral hinge 32 c. Each housing section 32 a, 32 b includes an innermembrane strip 34 a, 34 b joined along the sides and end wall of therespective tubular section to define two internal chambers 35 a, 35 b.The probe further includes an outer membrane 36 a, 36 b for each housingsection 53 b defining the two-section inner chamber 54 a, 54 b, and thetwo-section outer membrane 55 a, 55 b defining the two-section outerchamber 56 a, 56 b communicating with the inner chambers via openings57.

FIG. 11a further illustrates the two sensor elements 58 a, 58 b fixed tothe two inner membranes 53 a, 53 b, so as to be located at the oppositesides of the finger when received within the compartment defined by theprobe, as shown in FIG. 11b. The two sensor elements 58 a, 58 b areconnected by electrical conductors 59 to an electrical circuit 60 (FIG.12) fixed to a band 61, either directly connected, or by way of a glove.Electrical circuit 60, for example, could include the power supply andother circuitry for driving the sensor elements 58 a, 58 b, forreceiving the outputs of those elements, and for storing the outputs,e.g., in a storage device, so as to eliminate the need for externalelectrical connections when the device is being used.

FIG. 11a further illustrates the provision of a pressure-sensitiveswitch P, or other pressure sensing device such as a strain gage, oninner membrane 53 b, to ensure that leakage has not occurred, and thatthe appropriate pressure has been reached, when the probe is applied tothe subject's finger. The pressure sensing device could be connected inseries with the optical sensor, or in parallel to the control device.

While many of the drawings, such as FIGS. 4, 7 a-7 c, 8 a-8 c, 9 and 10a-10 c, do not include the sensor elements corresponding to sensorelements 6 a, 6 b of FIGS. 1 and 1a and sensor elements 58 a, 58 b ofFIGS. 11a-11 c, it will be appreciated that these are omitted merely forpurposes of simplifying the illustration and the description of theseprobes, and that such probes, when used for the particular applicationsdescribed above, would also include such sensor elements. As indicatedearlier, the sensor elements in all the described examples could beoptical sensors, e.g., a light source (LED) and a light receiver foroptically sensing the changes in the finger received within the probe;magnetic sensors, e.g., a permanent magnet and a magnetic field detectorfor sensing the changes in the finger girth by the Hall Effect; or othertypes of sensors, such as described in the above-cited PCT PatentApplication.

FIGS. 13a-13 c illustrate one manner of mounting the sensor elements 58a, 58 b in the finger probe, and making the external electricalconnections to the sensor elements. Thus, each sensor element 58 a, 58 bis connected at one end to an electrical conductor 59 a, 59 b, having arubber plug 62 a, 62 b, at the opposite end, to provide airtight sealsin order to preserve the above described Laplace behavior. Plugs 62 a,62 b are receivable within openings 63 a, 63 b in the walls of the twohousing sections 52 a, 52 b hinged together by the strip 44 of flexiblenon-stretchable material. The two sensor elements 58 a, 58 b are fixedto the two diaphragms 53 a, 53 b within the compartment defined by thetwo housing sections 52 a, 52 b, such that when the sensor elements areassembled, and the two housing sections are in their closed condition asillustrated in FIG. 13c, the two sensor elements engage the oppositesides of the finger received within the housing compartment. The sensorelements output signals, via the electrical conductors 59 a, 59 b whichpass through the housing wall, to the electrical processing and/orstorage system, such as the electrical circuit 60 (FIG. 12) on the band61 of the patient.

One of the plugs, e.g., plug 62 a, could be provided with the pressuresensing device P to ensure leakage does not occur, and that theappropriate level of pressure has been reached, when the probe isapplied, as described above with respect to FIG. 11a.

FIG. 14 illustrates a finger probe having a thimble section 72 forreceiving the end of the patient's finger 73 and an annular pressurecuff 74 contiguous to the open end of the thimble section 72 on the sidenearer the heart of the patient when the probe is applied to thepatient's finger. Such a pressure cuff extends the static pressure fieldpast the sensor elements 58 a, 58 b towards the heart side of thepatient as described in the above-cited PCT Application. In this case,an inner diaphragm 75 is attached around its periphery to the innersurface of the thimble section 72 to define therewith an inner chamber76; and similarly, another inner diaphragm 77 is attached around itsperiphery to the inner surface of the annular cuff section 74 to definetherewith an inner annular chamber 78. In addition, an outer diaphragm79 is attached along one side of its periphery to the outer surface ofthe thimble section 72 and along the other side of its periphery to theouter surface of the annular section 74, to define with both sections acommon outer chamber 80. The outer chamber 80 communicates with innerchamber 76 via openings 81 in the thimble section 72, and with innerchamber 78 via openings 82 in the annular cuff section 74.

The sensor elements 58 a, 58 b are located within the thimble section72. This section applies the static pressure field described earliersubstantially uniformly around the distal end of the subject's finger73. This static pressure field is extended past the sensor elementstowards the heart side of the patient by the inner chamber 78 defined bymembrane 77 of the annular cuff section 74 as described in theabove-cited PCT Application. In this case, however, the common outerchamber 80 defined by the outer membrane 79 maintains substantially thesame static pressure field in both the thimble section 72 and theannular section 74 despite changes in volumes therein, according to theLaplace Law as described above.

In the above-described probes, the sensor elements (e.g., 6 a, 6 b inFIGS. 1a, 1 b) are contained within the finger probe so as to be locatedon opposite sides of the patient's finger when inserted into the probe.In such arrangements, the sensor elements generate electrical signalswhich are outputted via electrical conductors to processing and/orstorage circuitry, e.g, electrical conductor 59 and storage circuitry 60in FIG. 12.

FIGS. 15 and 16 illustrate two arrangements wherein the sensor elementsare not located in the housing of the finger probe, but rather inanother housing separate from the finger probe and connected thereto byfluid tubes.

The probe illustrated in FIG. 15 is of the type illustrated in FIG. 14,including a thimble section 72 and an annular cuff section 74. The innerchamber 76 of the thimble section 72 is connected by a fluid tube 90 toa chamber 92 disposed within a second, rigid housing 93, which ispreferably mounted close to the finger probe, e.g., on the subjectswrist. Chamber 92 is defined by a cylinder 94 closed at one end by anend wall 95, and at the opposite end by a membrane 96.

Annular chamber 78 of the cuff section 74 is connected via another tube97 to another chamber 98 within the second housing 93. Chamber 98 isdefined by a cylinder 99 closed at one end 100 and at the opposite endby another membrane 101.

It will be seen that the two chambers 92 and 98 within the secondhousing 93 will be subject to the same pressures as chamber 76 in theprobe thimble section 72 and chamber 78 in the cuff section 74,respectively. These pressures will be opposed by the pressure within thesecond housing 93. The latter pressure may be preset by a syringe 102including a cylinder 103 coupled to the interior of housing 93, and aplunger 104 which is movable in order to change the volume, and therebythe pressure, within housing 93.

Chamber 92, connected via tube 90 to the thimble section 72 of theprobe, includes the sensor for sensing the volume changes within chamber76 of the thimble section 72, and thereby the physical condition of thepatient wearing the thimble. Thus, one sensor element 105 a is fixed tomembrane 96 so as to be displaced with that membrane, whereas the othersensor element 105 b is fixed to the bottom wall 95 of chamber 92, suchthat sensor elements 105 a and 105 b together can be used to measure thevolume changes within chamber 94.

Although, the FIG. 15 arrangement does not provide the advantage of thepreviously-described arrangements in having the pressurizing means, forapplying the static pressure substantially uniformly around the distalend of the patient's digit, to be constituted of a medium whollyself-contained within the finger probe, it does provide a number ofother advantages: Thus, the thimble section 72 of the probe in FIG. 15does not require an external chamber, as for example described withrespect to FIGS. 1 and 1a, since chamber 94 within the second housing93, if vented to the atmosphere, would act as the external chamber toprovide the probe with the above-described Laplacian P/Vcharacteristics. Also, if the housing is not vented to the atmosphere,this arrangement enables convenient presetting of the pressures in boththe thimble section 72 of the probe, as well as in the annular cuffsection 74.

This arrangement also simplifies the construction of the probe attachedto the patient's finger since it locates the sensor elements in theseparate housing 93 rather than in the probe itself. Thus, the thimblesection of the probe could include two pliable plastic tubular elementseach closed at one end and open at the opposite end, and located in thethimble section so as to engage the opposite sides of the patient'sfinger when inserted therein, such that each such element definesone-half of the pressurizing-chamber. Also, the cuff section 74 could beomitted.

Another possible advantage in the FIG. 15 arrangement is that it tendsto avoid local bias towards smaller superficial blood vessels. Alsohousing 93 containing the sensor elements 105 a, 105 b, can be locatedvery close to the finger-applied probe, such as on a wrist band (FIG.12) to minimize the restrictions in the mobility of the patient and alsothe length of the fluid tubes 90, 97.

FIG. 15a illustrates a variation in the construction of the apparatus ofFIG. 15, in that the separate housing 93 includes a pressure sensor 150which senses the pressure within that housing and feeds this informationto a CPU 106. The CPU 106 also receives information from the pressuresource 107 (e.g, the syringe 102 in FIG. 15) which presets the pressurewithin housing 93. The output signals from the sensor elements 105 a,105 b within housing 93, are also received by CPU 106 after theseoutputs have been amplified, filtered, and otherwise processed incircuit 108. The CPU 106 processes the foregoing inputs, e.g., asdescribed in the above-cited PCT Application, and produces an outputwhich is displayed in display 109.

In all other respects, the apparatus illustrated in FIG. 15 isconstructed and operates in the same manner as described above withrespect to FIG. 15, and therefore includes the same reference numeralsidentifying the corresponding parts.

FIGS. 16 and 16a illustrate a finger probe of the same construction asdescribed above, particularly as illustrated in FIGS. 15 and 15a, butincluding an adhesive layer to be contacted by the patient's fingerreceived within the finger probe. The adhesive layer is provided by adouble-sided adhesive strip 107, including an inner adhesive layer 107 aand an outer adhesive layer 107 b. The inner adhesive layer 107 a iscovered by a protective layer 108 which is stripped away, after thefinger has been inserted within the probe, to enable the inner adhesivelayer 107 a to contact and firmly adhere to the subject's finger whenreceived within the probe.

In all other respects, the probe illustrated in FIG. 16 and 16a may beof the same construction as described above, particularly with respectto FIGS. 15 and 15a.

FIG. 17 illustrates apparatus including the novel finger probe used inapparatus, similar to that described in FIG. 23 of the above-cited PCTApplication, for effecting continuous non-invasive blood pressuremeasurements. For purposes of example, the finger probe illustrated inFIG. 17 is shown as being of the construction described above withrespect to FIGS. 11a-11 c, although it will be appreciated that it couldbe of any of the other described constructions.

Thus, the finger probe illustrated in FIG. 17 includes an electricalheater winding 110 applied around the outer surface of the probe housing52 a, 52 b for heating the patient's finger within the internal chamber54 a, 54 b of the probe to any predetermined temperature, preferably35-40° C. A thermister 111 or the like controls the electrical heater inorder to maintain that temperature so as to dilate the blood vessels inthe finger.

The probe illustrated in FIG. 17 further includes a vertical positionsensor 112 for sensing the vertical position of the finger probe withrespect to a reference point. Sensor 112 may be of the same constructionas described in the above-cited PCT Application, including a housingfilled with a liquid (preferably water) closed at one end by a flexiblemembrane 112 a and connected at its opposite end via a water filled tube113 to a pressure transducer 114. Transducer 114 produces an electricaloutput corresponding to the vertical position of sensor 112, and therebyof the finger probe, with respect to the subject's heart level.

The previously-described sensor elements 58 a, 58 b of the finger probeare connected via electrical conductors 115 to a circuit 115 a foramplifying and processing the output signals, and via an A/D converter116, to the CPU 117. The electrical heater winding 110 is supplied withpower via conductors 118 connected to an electrical power supply 119,also supplying power to the CPU 117. Thermister 111 is connected viaconductors 120 to a control circuit 121, which also produces an outputto the CPU 117 via the A/D converter 116. CPU 117 produces an output todisplay 122.

The manner in which the apparatus illustrated in FIG. 17 is calibrated,and then used, for the continuous non-invasive blood pressuremeasurements is described in the above-cited PCT Application.

FIGS. 18a-18 d illustrate a further finger probe device including aself-contained pressurizing source eliminating the need for fluidconnections from the probe to an external source of pressurized fluid.In the probe illustrated in FIGS. 18a-18 d, however, the pressurizingsource for applying the static pressure to the patient's finger is notprovided by a fluid chamber within the finger probe as in thepreviously-described embodiments, but rather is provided by a body ofresilient sponge material within the finger probe.

Thus, the finger probe illustrated in FIGS. 18a-18 d includes a housing202 split into two half-sections 202 a, 202 b, hinged together along oneside by a flexible, non-extensible strip 203 and containing “Velcro”(T.M.) strips 204 at the opposite side for tightly clamping the probe tothe patient's finger 205 according to the static pressure to be applied.In this case, however, the means for applying the static pressure aroundthe patient's finger is in the form of a body of resilient spongematerial 206 a, 206 b, carried by each half-section of the probe. Alayer of a gel material 207 a, 207 b, covers the inner surface of eachof the sponge bodies 206 a, 206 b so as to be exposed for direct contactwith the patient's finger when inserted into the housing and the housingsections are in their closed condition as illustrated in FIGS. 18c and18 d. The sensor elements 208 a, 208 b, which may be any of the devicesdescribed above, are carried on the inner surfaces of each of the spongebodies 206 a, 206 b, or their respective gel layers 207 a, 207 b.

It will be seen that any desired fixed pressure may be applied to thepatient's finger within the probe by applying the Velcro strips with theappropriate tightness to the two housing sections around the patient'sfinger. The gel layers 207 a, 207 b more securely fix the sponge bodiesand their sensor elements to the finger end, and more evenly dissipatethe applied force.

While the invention has been described with respect to several preferredembodiments, it will be appreciated that these are set forth merely forpurposes of example, and that many other variations may be made. Forexample, other sensors could be used than the optical and Hall-Effectsensors referred to above, e.g., as described in the above-cited PCTApplication. Other fasteners than the “Velcro” or other types describedabove could be used. Also, the probe may be incorporated in a glove tobe worn by the subject as also described in the PCT Application.

Further, the finger probe could be used to house a pulse oximeter formeasuring the oxygen saturation of blood. In such an application,conventional pulse-oximeter sensors could be included in the probehousing and would produce a better measurement of the oxygen saturationof the blood (SaO₂) because of the stable environment provided by thestatic pressure field.

It will be appreciated that all the embodiments described with respectto FIGS. 1-17 could be designed to provide the above-described Laplaceoperation, wherein the distending pressure remains substantiallyconstant irrespective of changes in volume. While the probe constructionof FIGS. 18a-18 d, including the sponge cushion material, would notoperate according to the Laplace law it will be appreciated that ahybrid construction could be provided, wherein the sponge cushion isincluded to occupy only a part of the chamber containing the sensors andthereby to provide substantially the Laplace operation.

In addition, the invention could be used in applications other thanfinger probes, e.g., as a supplement to a wound dressing for a bodypart, as a means for producing venous distention in a body part inprepartion for venapuncture, as a means for supporting, decompressingand/or immobilizing soft tissue injuries like sprains in a wrist orankle, as a pressure applicatior for edematous regions in a body part,and the like.

Another possible application of the invention is as a disposable sensor,based on a preinflated surface mounted membrane or membranes, capable ofbeing applied to a finger by being wrapped around the finger and havinga free end adhesively closed to impart uniform pressure to the enclosedmass of the finger. The membrane(s) may be mounted on an airtightbendable, but nonstrechable, material such as plastic sheeting,rubberized cloth, or the like. A tube or tubes would communicate betweenthe finger probe and a sensing console which may be located at thewrist, for example. A unidirectional pressure release valve located atthe remote site would ensure that excess pressure is vented from thefinger probe upon its initial application.

A further possible application of the invention is in a verticaldisplacement sensor consisting of a single fluid filled tube connectedto an atmospheric pressure referenced pressure transducer at one end,and a compliant tip at the opposite end. The pressure transducer and thecompliant tip would be respectively situated at heart level and themeasurement site, or vice-versa.

A still further variation would be to provide the probe with thecombination of an optical sensor and a volumetric sensor within the sameprobe. The optical sensing elements need not be located on oppositesides of the finger as described, but could be at other locations. Oneparticularly useful arrangement is that in which optical sensor andlight source are respectively placed over the digital arteries, thusbeing oriented at about 140 degrees with respect to each other.

Many other variations, modifications and applications of the inventionwill be apparent.

What is claimed is:
 1. A device for application to a body part of apatient to determine the physiological condition of the patient,comprising a probe including: a housing defining a compartment closed atone end and open at an opposite end for receiving a distal end of thebody part including a terminal-most extremity; pressurizing means forapplying a static pressure field substantially uniformly around thedistal end of the body part, when received in said compartment,including the terminal-most extremity, which static pressure field is ofa predetermined magnitude sufficient to substantially prevent distentionof venous vasculature, uncontrolled venous backflow, and retrognadeshockwave propogation into said distal end, and to partially unload walltension of, but not to occlude, arteries in said distal end when atheart level or below; and a sensor for sending changes in said distalend of the body part related to changes in volume thereof due to changesin instantaneous blood volume related to arterial blood volume therein,wherein said pressurizing means for applying said static pressuresubstantially uniformly around the distal end of the body part,including the terminal-most extremity, comprises a medium whollyself-contained within said probe.
 2. The device according to claim 1,wherein said pressurizing means includes an inner resilient membranewithin said housing and defining therewith an inner chamber to be filledwith a fluid for applying said static pressure via said membranesubstantially uniformly around the distal end of the body part includingthe terminal-most extremity.
 3. The device according to claim 2, whereinsaid pressurizing means further includes an outer resilient membraneattached to said housing externally thereof and defining therewith anouter chamber communicating with said inner chamber via openings in saidhousing for enlarging an effective volume of said inner chamber such asto cause said inner membrane to apply substantially the same staticpressure around the distal end of the body part despite changes involume thereof.
 4. The device according to claim 3, wherein said housingincludes a port having a one-way valve for filling said inner chamber toa desired predetermined pressure.
 5. The device according to claim 3,wherein said outer resilient membrane is of annular configuration and isapplied around an annular portion of the housing formed with saidopenings providing communication between said inner and outer chambers.6. The device according to claim 3, wherein said outer resilientmembrane is of tubular configuration and is attached around an outer tipof the housing, said outer tip being formed with said openings providingcommunication between said inner and outer chambers.
 7. The deviceaccording to claim 6, wherein said housing includes an annular ringspaced from the outer resilient membrane attached to the housing forreceiving an open end of a syringe to be used for enlarging said outerchamber by shifting the fluid from said inner chamber to said outerchamber to facilitate insertion of the body part into said compartment.8. The device according to claim 6, wherein said outer resilientmembrane includes a finger piece graspable by a user for enlarging saidouter chamber by shifting the fluid from said inner chamber to saidouter chamber to facilitate insertion of the body part into saidcompartment.
 9. The device according to claim 8, wherein said fingerpiece includes a knob extending externally of the outer membrane forgrasping by the user and fixed to a backing member engageable with aninner surface of the outer membrane.
 10. The device according to claim3, wherein said housing is made of two sections hinged together toassume open and closed conditions, and including at least one fasteningelement for fastening the two sections in their closed condition. 11.The device according to claim 10, wherein said at least one fasteningelement is “Velcro” (T.M.) hook and loop fastener strips carried by thetwo housing sections.
 12. The device according to claim 10, wherein saidat least one fastening element is tongue and recess formationsintegrally formed in the two housing sections.
 13. The device accordingto claim 10, wherein said housing includes a tubular side wall closed atone end by an end wall and open at the opposite end, said tubularhousing being split into two half-sections and hinged together at saidend wall.
 14. The device according to claim 10, wherein said housingincludes a tubular side wall closed at one end by an end wall and openat the opposite end, said housing being split into two half sections andhinged together along said tubular side wall.
 15. The device accordingto claim 13, wherein said hinge is an integral hinge integrally formedwith said two half sections of the housing.
 16. The device according toclaim 13, wherein said hinge is a strip of flexible strechable materialattached to the two housing half-sections.
 17. The device according toclaim 13, wherein: said inner membrane includes a membrane strip joinedto the side wall and end wall of each housing section; and said outermembrane includes another membrane strip attached to an outer surface ofeach housing section.
 18. The device according to claim 1, wherein saidpressurizing means includes an adhesive layer within said compartment tobe contacted by the body part received within the device.
 19. The deviceaccording to claim 18, wherein said adhesive layer is on an innersurface of a plastic strip, an outer surface of the plastic strip havinganother adhesive layer, said plastic strip further including aprotective layer covering the adhesive layer on an inner surface thereofand strippable therefrom to enable said inner surface to contact andfirmly adhere to the body part when received within the device.
 20. Thedevice according to claim 1, further including an annular pressure cuffapplied around the body part contiguous to said housing on a heart sideof the patient to extend the static pressure field past the sensor onthe heart side of the patient.
 21. The device according to claim 1,wherein said pressurizing means includes a body of resilient spongematerial formed with a recess defining said compartment for receivingthe body part when inserted therein.
 22. The device according to claim21, wherein: said housing is made of two sections hinged together toassume open and closed conditions; said body of resilient spongematerial is also made of two sections, one carried on each of the twosections of the housing; and said two housing sections further includeat least one fastening element for fastening the two housing sections intheir closed condition.
 23. The device according to claim 22, whereineach of said two sections of the body of resilient sponge materialincludes a layer of a gel material exposed for contact with the bodypart when inserted into the two housing and the housing sections are intheir closed condition.
 24. The device according to claim 1, wherein apressure sensing device is located within said housing to sense thepressure applied to the patient's body part by said pressurizing means.25. The device according to claim 1, wherein said sensor is an opticalsensor and includes a light source carried within said housing on oneside of the body part when inserted therein, and a light detectorcarried within said housing on an opposite side of the body part. 26.The device according to claim 1, wherein said sensor is a Hall effectsensor and includes a permanent magnet carried within said housing onone side of the body part when inserted therein, and a magnetic fielddetector carried within said housing on an opposite side of the bodypart.
 27. The device according to claim 1, wherein said sensor comprisesa combination of an optical sensor device and a volumetric sensingdevice.
 28. The device according to claim 1, wherein said sensor is apulse oximeter sensor for sensing oxygen saturation of blood.
 29. Thedevice according to claim 1, further including electrical conductorsleading from said sensor to an electrical circuit carried by a bandapplied to another body part of the patient.
 30. The device according toclaim 29, wherein said electrical circuit includes a storage device forstoring an output of said sensor.
 31. The device according to claim 1,wherein the body part is a finger.
 32. A device for application to abody part of a patient to determine the physiological condition of thepatient, comprising: a first housing defining a first compartment closedat one end and open at the opposite end for receiving a distal end ofthe body part including a terminal-most extremity; pressurizing meansfor applying a static pressure field substantially uniformly around thedistal end of the body part, when received in said compartment,including the terminal-most extremity, which static pressure field is ofa predetermined magnitude sufficient to substantially prevent distentionof venous vasculature, uncontrolled venous backflow, and retrogradeshockwave propagation into said distal end, and to partially unload walltension of, but not to occlude, arteries in said distal end when atheart level or below; a sensor for sensing changes in said distal end ofthe body part related to changes in volume thereof due to changes ininstantaneous blood volume related to arterial blood volume therein; anda second housing separate and apart from said first housing and defininga second compartment having a fluid connection to said firstcompartment, said sensor being located within said second housing inoperative position with respect to said second compartment.
 33. Thedevice according to claim 32, wherein said second housing includes apresettable pressure source for presetting a predetermined pressureinside said second housing.
 34. The device according to claim 32,wherein said second housing is vented to atmosphere.
 35. The deviceaccording to claim 22, wherein the body part is a finger.
 36. A devicefor application to a body part of a patient to determine thephysiological condition of the patient, comprising: a housing defining acompartment closed at one end and open at the opposite end for receivinga distal end of the body part; a first membrane defining a first chambercontaining a pressurized fluid to apply a static pressure field to thebody part when received within the housing; a second membrane defining asecond chamber communicating with said first chamber and of a volumesuch that combined volumes of the first and second chambers maintain arelatively constant pressure despite changes in volume according to theLaplace Law; and at least one sensor element in at least one of saidfirst and second chambers for sensing changes in said distal end of thebody part related to changes in volume therein.
 37. The device accordingto claim 36, wherein said second membrane encloses at least a portion ofsaid housing to define said second chamber with an outer surface of anenclosed portion of the housing, said second chamber communicating withsaid first chamber via openings through said housing.
 38. The deviceaccording to claim 37, wherein said at least one sensor element iscarried by said first membrane in said first chamber.
 39. The deviceaccording to claim 37, wherein said second membrane is of annularconfiguration and is applied around an annular portion of the housingformed with said openings providing communication between said inner andouter chambers.
 40. The device according to claim 37, wherein saidsecond membrane is of tubular configuration and is attached around anouter tip of the housing, the outer tip being formed with said openingsproviding communication between said first and second chambers.
 41. Thedevice according to claim 36, wherein said second chamber defined bysaid second membrane is located in a second housing and is connected tosaid first chamber by a fluid tube.
 42. The device according to claim41, wherein said at least one sensor element is located in said secondhousing in operative position with respect to said second chamber. 43.The device according to claim 42, wherein said second membrane issubject to differential pressure with respect to the pressure in saidsecond chamber and ambient pressure in said second housing.
 44. Thedevice according to claim 43, wherein said second housing includes apressure presetting device for presetting the pressure within saidsecond housing acting on said second membrane.
 45. The device accordingto claim 44, wherein said second housing includes a pressure sensor forsensing the ambient pressure within said second housing.
 46. The deviceaccording to claim 36, wherein the body part is a finger.
 47. The deviceaccording to claim 42, wherein said at least one sensor translatesvolume changes in said second chamber into an electronic signal.
 48. Thedevice according to claim 47, wherein said at least one sensor comprisesa light source and an optical detector.
 49. The device according toclaim 48, wherein said light source is mounted on a movable membranewhich defines one wall of said second chamber and said optical detectoris mounted on a fixed base which forms another wall of said secondchamber, or vice versa, and wherein when said membrane shifts withrespect to said fixed base said optical detector emits a signal which isindicative of an amount of movement of said membrane and is correlatedto a volume change within said first and second chambers.